What is "fish"?

Fish are aquatic animals characterized by their streamlined body and scaly skin. They breathe through gills and use fins to swim in water. Fish are found in almost all aquatic environments, from freshwater rivers and lakes to saltwater oceans. They come in a wide variety of shapes, sizes, and colors, ranging from tiny minnows to large sharks. Some species of fish are edible and are consumed as a major source of protein by humans around the world. Fisheries are an important industry, providing food and livelihoods for millions of people, but overfishing and pollution have become major threats to many fish populations.